1. Field of the Invention
The invention relates to a throttle control apparatus of an internal combustion engine which operates to control a throttle valve so that the throttle opening amount matches a target throttle opening amount that depends upon an accelerator operated amount (i.e., an amount of depression of an accelerator pedal), and also relates to a throttle control method.
2. Description of Related Art
A known throttle control apparatus, as disclosed in Japanese Laid-open Patent Publication No. 9-42032, operates to appropriately control the throttle opening amount depending upon operating conditions of the engine as well as a driver's demand, by electronically controlling the throttle valve of the engine mounted in an automobile, or the like. In the throttle control apparatus, the output torque of the engine is controlled in response to a driver's demand in the following manner.
A target throttle opening amount is calculated based on an accelerator operated amount, i.e., an amount of depression of the accelerator pedal, and the opening amount of the throttle valve (throttle opening amount) is controlled to be substantially equal to the target throttle opening amount by means of an electric motor, or the like.
Under the above-described throttle opening amount control, the throttle opening amount increases or decreases with increases or decreases in the accelerator operated amount when the driver accelerates or decelerates the automobile, and therefore good driveability can be obtained without any problem. When the driver attempts to start more stable running of the vehicle in a steady-state operating mode upon completion of the acceleration or deceleration, however, the running conditions are not immediately stabilized, and the accelerator needs to be frequently operated in a repeated manner, with a result of deteriorated driveability.
Immediately after the accelerator operated amount undergoes a great change for acceleration or deceleration, for example, the throttle opening amount largely changes toward a target throttle opening amount that is set depending upon the accelerator operated amount, and the engine itself is also in the middle of transition from one operating state to another. It is therefore difficult to operate the accelerator pedal to such an accelerator pedal position that corresponds to a desired output torque so that the output torque is controlled to the desired level. Accordingly, the driver must frequently or repeatedly operate the accelerator pedal after the accelerating or decelerating operation, and thus sufficiently good driveability cannot be attained.
In the device disclosed in Japanese Laid-open Patent Publication No. 9-42032, when variations in the accelerator operated amount (the amount of depression of the accelerator pedal by the driver) are reduced, the control gain of the throttle opening amount is reduced based on the assumption that the automobile has been brought into a steady-state running mode, to thereby realize stable steady-state running of the automobile. However, the variations in the accelerator operated amount are reduced only after the running conditions of the automobile are sufficiently stabilized. In other words, the accelerator operated amount is still varied by a large degree during the transition from an accelerating/decelerating mode to the steady-state running mode. Thus, the throttle opening amount control cannot be started until after the accelerator operated amount is stabilized, and therefore the driveability cannot be improved.